Process for producing crimped polyester fibers of high modulus

ABSTRACT

A process for producing crimped polyester fibers of high modulus, which comprises drawing an undrawn tow of polyester to 1.15 to 1.45 times the natural draw ratio, heat-treating the drawn tow under tension at a temperature T1(*C.), feeding it into a stuffer crimper to crimp the tow while maintaining it at a temperature of 80* to 130*C., and heat-treating the tow at a temperature of T2(*C.) while allowing free shrinkage of the tow and maintaining the packing density of the tow at leat 200 Kg/m3, the T1 and T2 satisfying the relation specified in the specification.

United States Patent lzawa et a1. July 1, 1975 [541 PROCESS FOR PRODUCING CRIMPED 3,499,953 3/1970 Stanley 28/72.14 POLYESTER FIBERS OF HIGH MODULUS 3,553,803 l/197l Buschmann et a1. 28/72.l4 X

3,667,094 6/1972 Yazawa .1 28/72.14

1 Inventors: Nobuharu lmwa, Nlshikoizumi; 3,719,976 3 1973 lzawa et a1 .4 28/72.|4 Mutsuo Katsu; Yasuhiro Murase, T875,02l 6/1970 Addington et a1. 28/72 HR Takamitsu Kondo, all of Matsuyama, all of Japan Primary Examiner-Louis K. Rimrodt Attorney, Agent, or Firm-Sherman & Shalloway [57] ABSTRACT A process for producing crimped polyester fibers of high modulus, which comprises drawing an undrawn tow of polyester to 1.15 to 1.45 times the natural draw ratio, heat-treating the drawn tow under tension at a temperature T (C.), feeding it into a stuffer crimper to crimp the tow while maintaining it at a temperature of 80 to C, and heat-treating the tow at a temperature of T (C.) while allowing free shrinkage of the tow and maintaining the packing density of the tow at leat 200 Kg/m, the T, and T satisfying the relation specified in the specification.

3 Claims, 4 Drawing Figures loo PROCESS FOR PRODUCING CRIMPED POLYESTER FIBERS OF HIGH MODULUS This invention relates to a process for producing crimped polyester fibers of high modulus which have good spinnability and can be spun into yarns of superior quality.

Polyester fibers are widely used as spun fibers prepared either alone or in mixture with other fibers such as cotton, flax or rayon.

In order to enhance the spinnability of polyester fibers, it is the general practice to impart high tenacity, low elongation, and high modulus to the fibers. This can lead to some extent to high spindle speed which is most required in the overall spinning process. However, attempt to attain the high tenacity, low elongation and high modulus of the fibers in the manufacturing step inevitably results in the deterioration of crimp characteristics of the fibers and the extreme worsening of their spinnability in the pre-spinning step. Furthermore, the heat shrinkage of the fibers increases, and when the fibers are woven, the fabric is shrunken to a great extent during heat-setting to cause a reduction in weaving efficiency.

it is therefore an object of this invention to provide a process for producing crimped polyester fibers having superior crimp characteristics and low heat shrinkage in spite of having high tenacity and modulus.

According to this invention, there is provided a process for producing crimped polyester fibers of high modulus, which comprises drawing an undrawn tow of polyester to 1.15 to 1.45 times the natural draw ratio, then heat-treating the drawn tow under tension at a temperature T,(C. feeding it into a stuffer crimper to crimp the tow while maintaining it at a temperature of 80 to 130C and heat-treating the tow at a temperature of T-,(C.) while allowing free shrinkage of the tow and maintaining the packing density of the tow at at least 200 kg/m, the T, and T satisfying the following relation 1.25T 21 S T, 5 240 2.0T, 470 5 T 5 -0.5T, 210

The invention will be described in greater detail below with reference to the accompanying drawings in which:

FIG. 1 is a graphic representation showing the range of the heat-treatment temperatures T, and T FIG. 2 is a graphic representation showing the relation between the modulus at stretch (abbreviated as M 0f the fibers and the temperature T with the temperature T, used as a parameter;

FIG. 3 is a graphic representation showing the relation between the dry heat shrinkage at 180C. of the fibers and the temperature T with the temperature T, used as a parameter; and

FIG. 4 is a graphic representation showing the relation between the percent crimp of the fibers and the temperature T with the temperature T, used as a parameter.

The undrawn tow of polyester used in this invention is a bundle of undrawn filaments obtained by meltspinning a polyester-type polymer in a customary manner, and is usually used in a denier size of at least 10,000 denier, especially 50,000 to 4,000,000 denier.

The term polyester-type polymer or polyester", as used in the present specification and appended claims, denotes polyesters at least 85 mol of which consists of ethylene terephthalate units. Polyethylene terephthalate is used suitably as such as polyester. But in order to improve its dyeability or pilling resistance, it may contain copolymerized therein a third component such as isophthalic acid, para-hydroxybenzoic acid, or a glycol having at least 3 carbon atoms, or blended therein a small amount of other polymers such as nylon or a polyolefin. The polyester may further contain a delusterant, coloring agent, stabilizer, or antistatic agent, etc. The suitable intrinsic viscosity, as measured on an ochlorophenol solution at 35C., of the polyester is 0.50 to 0.70.

The first step of the process of this invention consist in drawing the undrawn tow of polyester to 1.15 to 1.45 times its natural draw ratio (NDR).

The natural draw ratio is measured as follows: An undrawn filament is allowed to stand for 24 hours in a chamber maintained at a temperature of 20 to 30C. and at a relative humidity of 50 to and then pulled at a rate of 1000 per minute in a chamber maintained at a temperature of 20C. and a relative humidity of 65 using an instron tensile tester. The draw ratio at which the neck of the filament disappears and the tensile stress abruptly increases is termed the natural draw ratio.

The natural draw ratio varies mainly according to the birefringence of the undrawn filament, but an undrawn filament prepared by a customary spinning technique usually has a natural draw ratio of 3.0 to 4.0. Accordingly, in the process of this invention, the undrawn tow having NDR of 3.0 is drawn to 3.45 to 4.35 times the original length, and when the NDR is 4.0, the undrawn tow is drawn to 4.60 to 5.80 times the original length.

Preferably, the drawing is carried out in a water or steam bath held at 60 to 100C. The drawing can be effected in one step. Especially, however, a two-staged drawing is preferred in which a first drawing is carried out in a water bath held at 60 to C. and a second drawing is carried out in a water or steam bath held at a temperature of at least 80C. Where the two-staged drawing is employed, it is generally preferred to adjust the draw ratio in the secon drawing to 1.05 1.2.

In any case, it is essential at the draw ratio be 1.15 to 1.45 times the natural draw ratio. If the total draw ratio is below this range, fibers of high tenacity and modulus cannot be obtained, and on the other hand, if the total draw ratio is above this range, the drawing condition becomes poor, and stable production is impossible.

The drawn tow is then heat-treated under tension. For example, this step can be performed by (a) causing the tow to run in contact with a hot plate, (b) causing the tow to run in a zig-zag fashion through, and in contact with, a plurality of heated rollers, or (c) passing the tow through a heated chamber. This heat-treatment under tension may be performed simultaneously with the second-stage drawing.

The term heat-treatment under tension", used in the present specification and claims, denotes heattreatment which is carried out while maintaining the tow under stretch or at constant length, or allowing the tow to shrink 5 or less.

The drawn tow which is to be heat-treated at a temperature T,C. in the process of this invention generally has the property of shrinking 5 or more at this temperature. Accordingly, when the tow is heat-treated under conditions which do not allow a shrinkage of more than 5 it is always under tension. If the shrinkage in this treatment is in excess of 5 the modulus of the tow decreases, and the crimp characteristics are drastically deteriorated.

Having regard to the free-shrinkage heat-treatment temperature (T,C.), this tension heat-treatment temperature (T,C.) must be in the following range 1.25 T +2l 5 T, 5 240.

HT, is less than (1.25 T, 21 polyester fibers of high modulus (a modulus at stretch of at least 3.0 g/d) intended by the present invention cannot be obtained. On the other hand, if T, exceeds 240C, partial meltadhesion of the fibers occurs during the treatment. Especially when it is desired to obtain high modulus low shrinking fibers, T, is preferably higher than 180C.

After this heat-treatment under tension, the tow is treated with oils, as required, and then crimped by a stuf'fer crimper at 80 to 130C. The temperature raise of the tow at the time of crimping can also be accomplished by preheating it with a steam bath or plate heater, etc. prior to crimping. Or this can be achieved by introducing heated steam into a stuffing box of the stuffer crimper. If the temperature of the tow during crimping is lower than 80C., the crimp characteristics of the resulting fibers are poor, and good spinnability cannot be ensured. If it exceeds 130C, the modulus of the product decreases, making it unsuitable for high speed spindle rotation in the spinning process. The optimum temperature of the tow in this crimping step is 90 to 120C. in order to maintain a good balance between the crimp characteristics and the modulus.

The crimped tow obtained is continuously forwarded through a chute, and placed on a conveyor, where it is heat-treated under free shrinkage.

It is necessary at this time to increase the packing density of the tow during treatment to 200 kg/m" or more which is far higher than that under ordinary conditions, by properly controlling the method of supplying the tow to the conveyor or the running speed of the conveyor. If this packing density is lower than 200 kg/m the crimps are stretched at the time of heat- 2.0 T, +470 5 T 5 0.5 T, +210 if T, is lower than 80C., the crimp elasticity of the tow decreases extremely, and therefore, the degree of residual crimp of the fibers under repeated stretch in the spinning step decreases greatly, which in turn results in poor spinnability. On the other hand, if the temperature T is below (2.0 T, 470)C., the dry heat shrinkage of the tow at 180C. exceeds 6 and low shrinkage fibers intended by the present invention cannot be obtained. When T is more than (0.5 T, 210)C., the crimp characteristics, especially, the percent crimp, of the fibers are deteriorated drastically, making it impossible to ensure good spinnability.

The range of T, and T specified in this invention is the hatched portion in FIG. 1. Lines A to E in FIG. 1 show the following equations, and the area surrounded by these lines is employed in the present invention.

A. .T,=l.25 T, 21, B T =-2.0 T, 470,

C. .T 0.5 T, 210, D T, 240,

The lines A, B and C in FIG. 1 show the critical conditions for obtaining the intended modulus, dry heat shrinkage, and crimp characteristics, respectively. The line D shows the critical conditions for avoiding the melt-adhesion of the fibers, and the line B shows the critical conditions for obtaining good crimp elasticity.

The process of the present invention as described above makes it possible to afford polyester fibers having high tenacity and modulus, low heat shrinkage and superior crimp characteristics by dint of a synergistic effect brought about by a combination of the drawing, crimping and heat-treating conditions described. For example, polyethylene terephthalate fibers obtained by the present process have an M (modulus at 10 stretch) of at least 3.0 g/d, a dry heat shrinkage at 180C. of not more than 6 and a percent crimp of at least 10 Depending upon the conditions, polyethylene terephthalate fibers can be obtained which have a tenacity of at least 6.5 g/d, an elongation of not more than 30 an M, of at least 4.5 g/d, a percent crimp of at least 10 a dry heat shrinkage at 180C. of not more than 6 and a crimp elasticity of at least These fibers are cut to suitable lengths to make staple fibers. When the staple fibers are spun either alone or together with other fibers such as cotton, rayon or flax, the lap licking, and fiber wrappings on a cylinder of a carding machine, etc. in the pre-spinning step are improved, and the spinning step can be operated at high speed.

For example, when a 65/35 mixture of commercially available polyester staple fibers with cotton is spun into a spun yarn of 45 count, the rotating speed of spindles in the spinning step is 16,000 rpm at the highest, and the tenacity (lea tenacity) of the spun yarn is 29 kg at the highest. In contrast. the staple fibers obtained in this invention do not cause any trouble even when the rotating speed of spindles is increased to 20,000 rpm, and the tenacity (lea strength) of the spun yarn can be increased up to 34 to 35 kg.

The following Examples illustrate the invention more specifically. The percent crimp, or the degree of crimp, of filaments was measured as follows:

The specimen filament of a given length (a) is placed under an initial load of 2 mg/denier. Then, a load of 50 mg/denier is exerted on the filament, and the length (b) of the filament is measured after a lapse of 30 seconds. The percent crimp is expressed by:

(b a)/b X 100 EXAMPLE 1 An undrawn tow (NDR=3.43) obtained by meltspinning polyethylene terephthalate having an intrinsic viscosity of 0.62 was drawn first to 3.90 times in a warm bath maintained at 70C., and then to 1.10 times in a warm bath held at C. The total draw ratio was 4.29 (1.25 times the NDR). Subsequently. the tow was heattreated under tension on a plate having a surface temperature of T,C. Then, the tow was heated with steam, and fed into a stutter crimper where it was crimped while maintaining it at a temperture of C. The tow withdrawn from the crimper was continuously led to a heat-treating chamber of the hot air circulating type and heat-treated under free shrinkage at T,C. while maintaining the packing density of the tow at 300 EXAMPLE 3 k 5 Run No. 2 of Example 2 was repeated by varying the The temperatures T, and T were varied in the above o mper ure at the time Of rimping, the mp raprocedure, and the M,,,, dry heat shrinkage at 180C. ture T and the packing density of the tow at the time and percentage crimp of the resulting fibers were meaof heat-treatment under free shrinkage. The crimp sured. The results obtained were plotted in F168. 2 to characteristics of the fibers obtained were measured, 4. and the results are shown in Table 2 below.

Table 2 Runs Nos. 4 5 6 7 8 9 T, (C.) 100 100 85 65 100 100 Tow temperature at time 95 95 95 95 I I0 65 of crimping ("C.) Pa gkin density (kgl- 175 230 230 230 350 l 350 I'll Numlaer of crimps per 13.5 l3.3 13.2 l3.4 13.5 13.3

Inc Percent crimp (701 7.4 11.9 12.7 13.2 13.1 7.9 Crimp elasticity (95) 75.3 73.3 71.0 64.5 74.8 72.3 Degree of residual 5.7 8.8 9.0 8.5 9.8 5.7

crimp ('5) Runs Nos. 4, 7 and 9 are comparisons.

lt is clear from the results shown in FIGS. 2 to 4 that EXAMPLE 4 fibers having an M of at least 3.0 g/d, a dry heat shrinkage at 180C. of not more than 6.0 and a percent crimp of at least 10 can be obtained only when An undrawn low of polyethylene terephthalate isothe temperatures T, and T, are within the range phthalate (containing 5 mol of isophthalic acid hatched in FIG. 1. units) having an intrinsic viscosity of 0.60 was drawn at EXAMPLE 2 a total draw ratio of 1.25 times the natural draw ratio 40 in the same way as in Example 2, Run No. 2. Then, the f f P y y tefepmhalale drawn tow was subjected the same heat-treatment 8 mmnslc of Obamed by y under tension, crimping, and heat-treatment under free tional melt-spinning, which had a natural draw rat o of Shrinkage as in Example 2 The fawning fib had a 3-43, was drawn in two stages at a 'f of monofilament denier of 1.26 denier, a tenacity of 6.68 1.10 to 1.25 times the natural draw ratio using a warm g/d, an elongation f 24.2 an Mm f 44 g/d, and a bath held at 70C. in the first-stage drawing and a warm dry heat Shrinkage at 180C. of 52 bath held at 90C. in the second-stage drawing. in each w we claim stage, the draw ratio was varied as shown in Table 1 be- L A process producing crimped polyester fib low. The dra o was caused t0 m 3 8- 8 fash' of high modulus, which comprises drawing an undrawn ion between heated rollers held at 195C. to heat-treat 5 tow f polyester m 5 to 145 times the natural draw it under tension, and then crimped 1n the same way 8 ratio, heat-treating the drawn tow under tension at a in Example The cnmped tow was 9 "9" temperature T,(C.), feeding it into a stuffer crimper to free shrinkage at l f of 100C while a crimp the tow while maintaining it at a temperature of mining the Packing dellslty of P tow at 300 kg/m' 80 to l30C., and heat-treating the tow at a tempera- The p p of resumng fibers are shown m 55 ture of T (C.) while allowing free shrinkage of the tow Table and maintaining the packing density of the tow at at m 1 least 200 kg/m, the T, and T, satisfying the following relation Runs Nos. 1 2 3 1.25 T, 21 5 T, S 240 (comparison) -2.0 T, 470 S T, S O.5 T, 210 1st stage draw ratio 3.78 3.90 3.56 2nd stage draw ratio L08 l.l0 I06 i T total draw ratio 4.08 4.29 3.77 0 total draw ratio/NOR 1.19 1.25 1.10 2. The process of claim 1 wherein the temperature of Monommncm den," L30 125 65 the tow fed to the stuffer crimper s to l20C. Tenacity (gld) 6.83 7.21 6.08 3. The process of claim 1 wherein T, is higher than Elongation (kl 25.9 23.4 33.5 1800C M, d) 4.6 4.7 4.1 Dry heat shrinkage 5.5 5.7 5.0

It ISO'C. (bl 

1. A PROCESS FOR PRODUCING CRIMPED POLYESTER FIBERS OF HIGH MODULES, WHICH COMPRISES DRAWING AN UNDRAWN TOW OF POLYESTER TO 1.15 TO 1.45 TIMES THE NATURAL DRAW RATIO, HEAT-TREATING THE DRAWN TOW UNDER TENSION AT A TEMPERATURE T1(*C.), FEEDING IT INTO A STUFFER CRIMPER TO CRIMP THE TOW WHILE MAINTAINING IT AT A TEMPERATURE OF 80* TO 1.30*C., AND HEAT-TREATING THE TOW AT A TEMPERATURE OF T2(*C) WHILE ALLOWING FREE SHRINKAGE OF THE TOW AND MAINTAINING THE PACKING DENSITY OF THE TOW AT AT LEAST 200 KG/M3, THE T1 AND T2 SATISFYING THE FOLLOWING RELATION 1.25 T2 + 21 T1 243 -2.0 T1 + 470 T2 -0.5 T1 + 210 80 T2.
 2. The process of claim 1 wherein the temperature of the tow fed to the stuffer crimper is 90* to 120*C.
 3. The process of claim 1 wherein T1 is higher than 180*C. 